Field of the Invention
This invention relates to the installation of everting flexible borehole liners into boreholes in geologic formations with shallow water tables or in geologic formations exhibiting artesian hydraulic head conditions.
Background
A “borehole” is a hole, e.g., a shaft or well, drilled into the Earth's subsurface. The hydraulic conductivity profiling techniques described in U.S. Pat. No. 6,910,374 and U.S. Pat. No. 7,281,422 have been used in over 400 boreholes since 2007. These patents, whose complete teachings are incorporated herein by reference, describe methods for determining the hydraulic transmissivity profile of the geologic formations surrounding borehole by carefully measuring the eversion of a flexible borehole liner into an open, stable, borehole. Other installations of flexible liners into boreholes, by the eversion of the liners, are disclosed in a number of other patents, such as U.S. Pat. Nos. 6,283,209, 6,794,127, and 7,896,578, obtained by this inventor. Such liners are usually installed into the open boreholes using a water level inside the liner which is significantly higher than the water table in the formation penetrated by the borehole.
However, when that required excess pressure head (difference between ambient water table level and water level supplied to the liner interior) is not available at a particular borehole, a scaffold plus an extension of the surface casing may be used to achieve the needed higher water level within the liner. In some situations of very shallow water tables, or in situations where the head within the borehole would rise above the ground surface if the surface casing were extended above the surface, the required scaffold is so high as to be very inconvenient or even dangerous, and use of scaffolds often exposes the installation personnel to freezing winter winds.
With the foregoing background, the presently disclosed invention was developed.